This invention relates to apparatus in continuous caster mold assembly for measuring friction forces on the mold during casting, and particularly to apparatus for minimizing the effects of tilting and imbalance of the mold on measuring devices used to estimate friction forces on the mold.
The process of continuous casting involves pouring molten metal into an open-ended mold having liquid cooled mold walls. A solidified skin forms adjacent to the mold walls while the metal is in the mold. The partially solidified casting is continuously withdrawn from the mold and passes through roll containment racks where it is spray cooled until complete solidification is obtained. The mold is oscillated in reciprocating fashion back and forth in the direction of casting so as to reduce friction between the mold walls and the skin formed adjacent thereto. Excessive friction forces cause defects in the casting and in severe cases results in tearing leading to a breakout of molten metal through the skin below the mold. Breakouts require shutdown and extensive repair or replacement of the roll containment racks before resuming caster operation. It is known to monitor friction forces in the mold during casting and to vary the cooling rate, speed of casting and other factors in order to avoid breakout. Examples of systems for this purpose are disclosed in British Patent 1,556,616, European Patent 44,291, U.S. Pat. No. 3,893,502 and Japanese Kokai J57032864. However, it has been difficult to obtain an accurate measure of such friction forces, decreasing the effectiveness of breakout avoidance systems based on present measurement apparatus. One of the problems involved is that it is difficult to separate the friction forces from other dynamic effects occurring during casting. These dynamic effects are quite variable and may not have any relationship to mold friction so that an accurate measure of friction force is not obtained. Various methods have been used for analyzing the indications obtained from load measurement apparatus in an attempt to separate out the dynamic effects and more accurately estimate mold friction. Examples of such methods are disclosed in U.S. Pat. No. 4,532,975 and U.S. Pat. No. 4,615,375. One of the significant dynamic effects involved is tilting and imbalance of the mold as it is oscillated during the actual casting operation. U.S. Pat. No. 4,532,975 and Japanese Kokai J57032864 recognize this factor but do not attempt to correct the influence it may have on friction force measurements. Misalignment and tilting of the mold during oscillation causes lateral forces of varying degree which significantly effect load cell readings. Generally, the load cells are designed to read only the vertical forces. European patent 44,291 discloses load cells that are movable in slots but which are secured in position by screw connection to a support plate. On the other hand, U.S. Pat. Nos. 4,219,091 and 3,741,328 are directed to load cell apparatus permitting lateral expansion and movement of a weighing device. Neither these references, nor any of the other prior art of which Applicant is aware, recognizes the need for counteracting the effect of tilting or misalignment of a continuous caster mold on friction force measurements or suggests a solution of that problem.
Therefore, it is a primary object of this invention to provide apparatus which will minimize the effect of tilting or imbalance of a continuous caster mold on mold friction force measurement made during actual caster operation.